Device for the frequency modulation of the resonant frequency of cavity resonators



e 24. 1948- J. o. H. FREDHOLM ET AL 2,435,649

DEVICE FOR THE FREQUENCY MODULATION OF THE RESONANT FREQUENCY OF CAVITY RESONATORS Filed Nov. 24, 1943 2 Sheets-sheaf. 1

rllln VENTorQS Patented Feb. 24, 1948 UNITED STATES PATENT OFFICE DEVICE FOR -THE FREQUENCY MODULA- TION OF THE RESONANT FREQUENCY OF CAVITY RESONATORS Johan Olof Helge Fredholm, Alsten, and Per Harry Elias Claesson, Jakobsberg, Sweden, assignors to Nils Georg Schonander, Stockholm,

Sweden Application November 24, 1943, Serial No. 511,522 In Sweden May 7, 1942 2 Claims. (01. 250-17) 'The present invention refers to a device .for periodic changes of the frequency or for frequency modulation of the resonant frequency of cavity resonators, for example in connection with elec- 2 Fig. 5 shows still another device for the same purpose.

Fig. 6 diagrammatically shows a Klystron provided with a device for the frequency modulation tron tubes comprising one or a plurality of cavity 5 of the basic frequency of the Klystron and for the resnators stabilizing of the said basic frequency.

The invention consists in a device for the fre- In Fig. 1 and Fig. 2 the rhumbatrons l and 2 quency modulation of the resonant frequency of are provided with connecting adjacent cavities 3 cavity resonators comprising metallic Walls for nd 4 in which the movable metal pistons 5 and electromagnetic waves and comprising a num- 5 h their rods 1 and 8 are located. The piston ber of cavity resonators, in which the cavity reso e provided with teeth which are arranged onator or a compartment adjacent said cavity to engage the teeth of the gear-wheels :3 so that resonator, or an inductance and/or a capacity is the piston rods with their respective pistons can constructed, arranged and operated periodically be moved backwards. The gear wheels l3 are only to increase and decrease its normal volume, int y p OVIded with teeth for the control of the ductance and/or capacity at resonant frequency on rods. When the teeth of the gear wheels in ste with the desired frequency modulation. loose then" ment W h th th f t p s- This increase and decrease of the volume ofa gfg gg r ife gdsnghtherpistfns are mgvedort-a vit c n be caused in various ways, for exam- S a s e s 1 a springs an Si e b; m echanical devices or electrically by ionizpressing the scs 5 I attached to said rods uning a gas within the cavity, by means of which 11116 10 5 e h t t d posl n marked the active volume disposable for oscillations w(iithg5: g a -i zglheels 3 are located on a rotating r e in gi f g flg g fffi gfi Increased and dec eas shaft M with the rotor [5 inside an airtight cavity The invention is particularly suitable for the g i l rgcatmg) with thefcaVtlgtls ai and 4, Th frequency modulation of ultrashort radio wave P fi g ygeanso as 15 12 2 011ttransmitters for television, telephony and other 51 e g g e i r g the purposes, when it is important in a simple way to i or can y y e concen con w frequency modulate the transmittedwave. In Fig. 2 the cavity resonator I s t cally According to the present invention 1t 15 pos closed y means of the g s p is throu h sible in a single step to cause a greater change of which the cencentric conductor 1 8 g s the giegliggclydihlagaghat has been possible by means jacent cavity 4 j glass plug '9 is located in According to an embodiment of the present ing sig gggg iag to the Wavedength of the vention it is possible simultaneously with the fre- Due to a certain factor of couplin between the quency modulation in a simple way to stabilize the cavity resonator I and the adjacerglt cavity 4 a resonant frequency of the resonatorgT Variation of the resonating frequency of the res Heretofore Separate frequency Sta {mug {mans onator I is obtained by variation of the volume have been used, for example a special oscillator 40 of the outside Cavity 4 controlled by a quartz crystal in order to keep the By frequency moduiatmn according to the pres-r mean Value of the carrier frequency abo1ute1y ent invention it is more convenient to vary ,the constant. Another method uses a particularly Volume of a Small cavity a greater percentage of complicated method of synchronizing by means its volume than to Vary the volume of a larger ofaseparately Furled "F cavity with the same volume-variation, because The present invention and its operating is furin such a Way a great change of the basic ther described in connection with the accompanyquency of the cavity is obtained mg drawings of which: In Fig. 3 and Fig. 4 the same numerals are used 1 shows a diag a View f an Q for similar parts. Instead of pistons cam-shaped lator of Klystrontype with Cavities of ble discs 20 of metal or of other suitable material, Volumes p ed to the rhumbatlonsfor example hard rubber, are adapted to rotate in 2 shows another embodiment as partof a cavities 2|, connected to the corresponding cavity construction similar to that shown in Fig. 1. resonators. Upon the rotation of the shaft M Fig. 3 and Fig. 4 show another device for the with the disc 20 the volume of the additional cavvariation of the volume of a cavity. ity 3-2l will vary according to a certain function.

In Fig. 5 the cavity resonator 22 is connected to the cavity 23-24 and provided with a bent spring 26, one end of which is provided with a piston 25, and the other end being fastened to a bushing- 21, attached to one end of the cavity 24. The spring 26 is adapted to be operated by an electromagnetic device, for example the electromagnets 2'8 and 29 outside the cavity 24, whereby the sprin 25 and the piston 25 can be caused to vibrate. The volume of the cavity 23 is thereby increased and decreased and thus the basic frequency of the cavity resonator 22.

In Fig. 6 which shows a frequency modulated ultrashort wave radio transmitter with a stabilising device for the basic frequency of the transmitter, the cavity resonators 3 l and 32 form parts of a Klystron device with additional cavities 33 and 34 respectively. In said cavities there are provided the pistons 35 and 36 movably attached to bent springs 31 and 38 so that the volumes of the auxiliary cavities can be varied when the pistons are moved to and fro. The springs 31 and 38 are normally arranged to vibrate by means of the electromagnets 39-40 and ll-42, which are fed with alternating current from the transformer 93 and cooperate to move springs 31 and 38, respectively, in one or the other direction.

According to the present invention a perfect stabilisation of an ultrashort wave transmitter is obtained by means of tuned cavity resonators of any type, for example of the rhumbatron-type as shown in Fig. 6, whereby one or two rhumbatrons 46-41 and Li849 are arranged in bridge connection, whereby the dipole 5| is connected to the common concentric conductor 50, said dipole be-- ing located in the neighbourhood of the energy output 43 of the transmitter to be controlled.

The bridge connection on the other side is connected in series with the diodes 52 and 53 or with bolometer receivers to the respective grids 55 and 56 in the double amplifier 54.

The anodes 51 and 58 of the said double amplifier are connected to the corresponding windings 6ll62 and iii-93 of polarized relays by means of which the springs 38 and 31 respectively are actuated.

The series-coupled resonators 4641 on one side of the bridge are tuned to a frequency (fr-f2) which with an amount of f2 varies from the desired basic frequency in The seriescoupled resonators in the other side of the bridge are tuned to a frequency n l-f2. I

The device operates in the following way. If

the dipole 5t is placed near the emitted energy from the transmitter 3l32, supposed to operate at a basic frequency ji, different amounts of wave energy pass through the parallel bridgearms 49-41 and 43-49 to the diodes 52 and 53 respectively, but only if the basic frequency differs from ii. In such a case more current passes through one diode than through the other, and after amplification in the tube 54, the windings 62 and 63 are more actuated than the counterdirected windings 60- -6l, whereby the springs 38 and 31 are pulled towards the relay cores B2 and 63 respectively. Hereby the cavities 34 and 33 are increased until the basic frequency again equals f1.

According to the present invention the average basic frequency can thus be kept constant at the same time that frequency modulation takes place about the said average basic frequency.

We claim:

1. A device for modulating the resonant frequency of an ultra short wave generator, a cavity resonator associated with said generator and comprising anauxiliary chamber in communication with said cavity, a member displaceable insaid auxiliary chamber to vary the active volume thereof, and means for rhythmically displacing said member in said chamber to increase and'decrease said active volume and thus the basic mean frequency of the cavity resonator in step with the frequency modulation impressed upon the sama'part of said auxiliary chamber being formed asa' plunger casing and said displaceable member is a plunger reciprocable in said casing, said means for displacing said member including a spring in said chamber bent at right angles to form two legs, the end of one of said legs being mounted in a wall of said chamber and the end of the other leg supporting said plunger, and electromagnetic means outside said chamber for cooperation with said first mentioned leg of said bent spring.

2. A device for modulating and stabilizing the basic mean frequency of an ultrashort radio wave transmitter, a cavity resonator associated with said transmitter, said device comprising a chamber containing an active volume normally associated with said cavity resonator, means to vary the active volume of said chamber, biasing means including a source of alternating current and two co'unterconnected' relay windings connected thereto for actuating said volume varying means, two separate sets of equal cavity resonators coupled in bridge connection, a common dipole at one end of the bridge to receive radio energy from the transmitter, and a double triode rectifying device having its grids connected to the other ends of said two separate cavity resonator sets, respectively, the two anodes of said double triode being coupled, respectively, to said two counterconnected relay windings of said biasing means, one of said separate sets of cavity resonators being tuned a little below and the other set being tuned a little above the basic mean frequency of the transmitter.

J OHAN QLOF HELGE FREDHOLM. PER HARRY ELIAS CLAESSON.

REFERENCES CITED The following references are of record in the file of this patent:

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